Spray paint guns spray paint from a nozzle with compressed air onto a surface being painted. In order to optimize the quality of the finish of the painted surface, it is important that the nozzle not be placed too close to the surface being painted. Placing the nozzle too close to the surface can cause an uneven wet film build as well as runs. It is generally desired that the coat of paint on the surface have uniform thickness at a thickness sufficient for complete coverage of the surface. The quality and uniformity of the paint coverage typically improves as the distance between the spray nozzle and the surface being painted increases.
It is also not desirable that the spray distance between the nozzle and the surface being painted be substantially larger than an optimum spray distance. Letting the spray distance be too large can cause overspray, paint fogging, or otherwise decrease the efficiency of paint transfer onto the surface being painted. Having the nozzle too far from the surface being painted not only increases the number of coats necessary to provide a sufficient wet film build for proper paint coverage, but also increases the cost of complying with environmental regulations. High levels of overspray and fogging increases the amount of volatile organic compounds that can escape from spray painting booths, and also increase the amount of hazardous waste that must be disposed of from spray paint system air filtering systems.
Depending on the type of spray painting system being used (e.g. conventional compressed-air system, electrostatic system, etc.), the type of paint being used, and possibly other factors, the optimum distance between the nozzle and the surface being painted varies. Several manufacturers and others in the industry have published data on what is believed to be the optimum spray distance based on a variety of factors. Even with knowledge of the optimum spray distances under each of the various conditions, it can be difficult for a person using a spray gun to keep the distance between the nozzle and the surface being painted at the optimum spray distance. This is especially difficult for novices.
It is generally believed in the spray paint industry that the optimum spray distance should be such that a fifty--fifty overlap of successive paths of spray paint provide sufficient wet film build for proper paint coverage. For novices and sometimes even experienced spray painters, it is difficult to maintain the proper spray pattern to obtain a concise fifty--fifty overlap, especially while trying to maintain the proper spray distance.